1. Field of the Invention
This invention relates to an optical multiplexer-demultiplexer device, also called a "muldex", enabling a mixing or separation of two optical signals carried by optical fibers, in other words a multiplexing or demultiplexing of two wavelengths.
When the device operates as a multiplexer, it combines in one optical fiber at least two optical signals having different wavelengths, propagated in two optical fibers. A multiplexer thus has two inputs and one output. Conversely, when the device operates as a demultiplexer, it separates two optical signals propagated in a same, single optical fiber and having two different wavelengths, each of the signals being fed to one of two output fibers. A demultiplexer thus has one input and two outputs.
Optical multiplexer-demultiplexer devices are used in particular for video or other telecommunications purposes in optical fiber cable distribution networks in which specific signal wavelengths are assigned to subscribers or groups of subscribers.
2. Description of the Prior Art
Specifically, the invention pertains to an optical multiplexer-demultiplexer device comprising ends of first, second and third optical fibers forming one of arms, a stem and another arm of a T pattern, respectively, and a dichroic filter disposed across the top of the T pattern. such a device called a "fiber optic coupler" is described in U.K. patent application No. 2,069,173.
The steps in the fabrication of such a coupler are as follows. An intermediate section of a single optical fiber intended to serve as the first and the third optical fibers is mechanically and chemically stripped; the stripped length of fiber is potted in an epoxy resin included in a mold. The potted fiber is cut in half at an angle of 45.degree. to its axis in the stripped section. After suitable polishing, grinding and cleaning, the endface of at least one of the first and third fibers thus cut at 45.degree. is coated with several dichroic layers and a dielectric material to form the dichroic filter.
Thereafter the two cut faces of the two molded supporting parts are assembled so as to align the first and third optical fibers by means of a conventional three-axis micrometer positioner and optical power measuring device. The fiber endfaces are bonded together with heat-setting epoxy resin, which is then heat cured. Lastly, the support so obtained is drilled in a direction perpendicular to the ends of the first and third optical fibers in order to coat with epoxy in the drilled hole a stripped and suitably prepared end of the second optical fiber.
Such a device is realizable in a factory but is difficult to fabricate at a works site due to the complex, fragile and bulky means employed. The cutting and polishing operations in particular are very difficult and the assembling of the two molded supporting parts requires considerable skill.
Moreover, when such a device is destined to couple three optical fiber ends forming part of a calbe or cables, it is necessary to connect the three ports of the device to the ends of the cable optical fibers by means of fiber-to-fiber connectors, so increasing the cost of the coupling and duration of the coupling operations. Indeed, in the prior art device, the ends of the first and third optical fibers to be coupled to establish a transmission path are derived from a single cut fiber.